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Here you will fine information about Altantoaxial Instability.
Atlantoaxial instability is a condition in which the first two cervical (neck)
vertebrae are not firmly attached. Normally, the atlas (the first cervical vertebra) and the axis (the second cervical vertebra)
are attached by a group of ligaments. They are further stabilized by a prominence on the axis called the dens that protrudes
into a hole in the atlas.
Dogs with congenital atlantoaxial instability are born without ligament support to their
atlantoaxial joint, and may also be born without a dens. Trauma to the neck can also cause tearing of the ligaments or fracture of the dens, resulting in atlantoaxial
instability.
Atlantoaxial instability can lead to cervical spinal cord injury
, the symptoms of which include: neck pain; a drunken, staggering gait; paralysis of all four legs; or sudden death.
Causes
Breeds at risk for congenital atlantoaxial
instability include all toy breeds, especially Chihuahuas, Pomeranians, Pekingese, toy poodles, and Yorkshire terriers. These
dogs usually show signs at less than one year of age, and symptoms can occur after very mild trauma, such as jumping off furniture,
which would be considered normal activity.
Any dog, young or old and of any breed, is at risk for atlantoaxial instability
after a traumatic event, such as being hit by a car or being an unrestrained passenger in a car accident.
Diagnosis
Your veterinarian will ask you many questions to develop a complete history
of the progression of the problem. These questions will include: what is your pet's age, was there any traumatic event, what
symptoms have you noticed, how long have they been going on, what treatments have you tried and with what results?
Your veterinarian will also examine your pet completely, including a neurological
examination to determine the severity of the problem as well as localize the level of the spinal cord injury.
Radiographs (X-rays) are usually taken to identify abnormal positioning
of the atlantoaxial joint.
Treatment
Medical treatment. Conservative management consists of several weeks of
cage rest to allow scar tissue to form, stabilizing the atlantoaxial joint. Steroids are also given for a short time to decrease
inflammation of the spinal cord. A neck brace is often used to minimize movement of the neck.
Surgical treatment. There is a high rate of recurrence of symptoms with
conservative management, so surgery is often recommended. Surgery is done either to stabilize the joint with pins, cement, wire, or suture,
or to fuse the joint. The type of surgery performed depends on the preference of the surgeon. After surgery, the care is similar to conservative management. The prognosis depends on the severity
of the neurologic signs before surgery.
Home Care
After surgery, the pet should be cage-rested and restricted
from activity for about 4 to 6 weeks. Frequent re-check examinations by your surgeon are necessary to identify potential problems
and correct them as soon as possible.
Dogs with this condition should not be bred, since there may be a genetic component
to this condition.
The neck is made of seven vertebral bones, or cervical vertebrae, which are connected by ligaments.
Each vertebra fits precisely with its neighbor to form a joint. The spinal cord is located in a tunnel within the vertebrae,
where it is protected from injury.
The first cervical vertebra is called the atlas; it holds up the head like Atlas held up the
world. The second cervical vertebra is called the axis. The atlantoaxial joint is held in place by several ligaments and by
a bony prominence of the axis called the dens, which fits in a hole in the atlas.
If the ligaments or the dens do
not develop correctly or are injured, the atlantoaxial joint becomes unstable. This places the delicate spinal cord at risk
for injury. Symptoms of spinal cord injury vary with the severity of the injury. Dogs with mild cases may only show neck
pain
. Those with more severe cases can have an unstable, wobbly, drunken gait.
And those with very severe cases can be completely paralyzed in all four legs, or suddenly die.
Death is often due to injury to the respiratory center in the spinal cord, making the animal stop breathing.
Congenital
atlantoaxial instability is usually seen in toy breeds less than one year of age. Breeds most often seen for this problem
include the Chihuahua, Pomeranian, Pekingese, toy poodle, and Yorkshire terrier.
Dogs with congenital atlantoaxial
instability are born without proper ligament support of their atlantoaxial joint, or are born without a dens, or both. The
instability that is present can predispose the dog to a major spinal cord injury with only a minor incident, such as jumping
off a piece of furniture.
Atlantoaxial instability can also develop in any dog after a major traumatic event, such
as getting hit by a car or being an unrestrained passenger in a car accident.
Diagnosis
History. Your veterinarian will ask you many questions regarding the development
and progression of the problem. Your pet's age is important to know, as well as any history of trauma to the pet. If other veterinarians have done any X-rays, then you should bring these results to your
veterinarian's attention. If you have tried any treatments for this problem, it's helpful to tell your veterinarian about
them and whether they have had any effect or not.
Physical exam. Your veterinarian will perform a complete physical exam.
He/she will watch your pet as he walks (if he can walk) to identify any abnormalities in his gait. Then the veterinarian will
perform a complete neurological examination to determine the severity of the injury and to localize the level of the spinal
cord that is affected. He/she will also listen to your pet's heart and lungs, take his temperature, and palpate your pet's
abdomen to be sure there are no other problems.
Blood and urine tests. If your pet will be undergoing anesthesia and surgery, blood and urine tests are run to be sure that he is not anemic and that he doesn't have any underlying
liver or kidney problems that might make anesthesia risky.
Radiographs (X-rays). X-rays are taken of the neck to identify the abnormal
positioning of the atlantoaxial joint, and possibly to identify the absence of a dens or any fractures of the bones. These
X-rays are often taken under general anesthesia to obtain the best position of the neck to identify the structures of interest.
The doctors and technicians must be very careful when moving the neck of these patients, since further damage can be done
to the spinal cord if sudden, extreme movements are made.
Conservative Treatment
The goal of conservative management
is to allow scar tissue to form around the atlantoaxial joint to stabilize it. Motion of the joint prevents scar tissue from
forming, so motion is prevented by placing a neck brace on the dog and by confining it to a cage for several weeks.
The
injury to the spinal cord results in inflammation. This can be reduced by the short-term use of steroids.
Most cases
managed in this way have a recurrence of symptoms, since the scar tissue is not strong enough to hold the joint stable.
Surgical
Treatment
Surgery is usually recommended for this problem due to the high recurrence rate with conservative management.
The goal of surgery is to stabilize the joint using internal devices. These can include wires, pins combined with an epoxy-like
cement, or heavy-duty suture material. The joint can also be fused, using screws and bone grafts collected from the dog's
shoulder.
Surgery is very difficult due to the small size of the patient and delicate nature of the bones. After surgery,
cage rest, neck braces, and steroids are often used as you would for conservative management.
There is less of a recurrence
rate when surgery is performed, but recurrences can still happen due to failure of the implants placed in the bones or failure
to follow post-operative instructions. The type of surgery depends on the surgeon's preference and the specific injury.
The prognosis depends on the severity of the neurological
signs present before surgery. The more severe the signs, the more guarded the prognosis. The spinal cord is an unpredictable
organ. Accurate predictions are difficult to make as to how much function will recover as well as how long it will take to
recover.
Follow-up
Atlantoaxial instability is a serious problem that requires dedicated and observant owners.
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical,
especially if your pet does not rapidly improve.
Administer all prescribed medications as directed. Alert your veterinarian
if you are experiencing problems treating your pet.
Follow your veterinarian's instructions for exercise restriction. The tissues must heal strongly to allow the joint to become stable. Excessive activity
can lead to tearing of healing tissues and cause a major setback.
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